How does freeze-thaw affect solvent-based paints?

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Canadian Paint and Finishing, 41, 3, pp. 38-39, 1967-05-01

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How does freeze-thaw affect solvent-based paints?

O'Doherty, G. A.; Ashton, H. E.

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TH1

N21r2

no. 314

c.

2

NATIONAL RESEARCH COUNCIL O F CANADA

L..

CONSEIL NATIONAL DE RECHERCHES DU CANADA

,-

H O W DOES FREEZE/THAW AFFECT SOLVENT-BASED PAINTS

by

G. A. O'DOHERTY AND H. E. ASHTON

Reprinted from

Canadian Paint and Finishing

Vol. 41, No.

3,

March 1967

Research Paper

NO.^^

14

of the

Division of Building Research

OTTAWA

May 1967

How does f reezelthaw affect

solvent- based paints?

0 Almost all studies of the effect of low temperatures o n

paint stability have been devoted to water-based coatings, particularly latexes. F r o m time to time, however, the question comes up whether solvent-based coatings are af- fected to any extent by low temperatures. It has ~ ~ s u a l l y been answered o n theoretical grounds that there should be no effect because the freezing point of most solvents is lower than the lowest temperatures experienced in Can- ada. Nevertheless, a practical answer is of some impor- tance to Canadian paint manufacturers because of the severe winter climate of most parts of Canada. This pa- per summarizes information obtained from trials run to determine whether solvent-based coatings are seriously af-

fected by storage in northern regions.

PROCEDURE-Fifteen alkyd enamels, four exterior paints and three lacquers were subjected to -50 1 5 ° F in a test cabinet. Each material was initially divided into two samples. One was placed in continuous frozen stor- age for 2 weeks; the other was subjected to a 48-hour cycle of 24 hours freezing and 24 hours at room teni- perature, also for 2 weeks. After normal laboratory stor- age of about 10 months, the materials were again ex- posed to their respective low temperature tests (some had to be excluded because of insufficient quantity for test) Most samples that had been stored continuously at -50°F were then subjected for 2 weeks to a severe (,-hour cycle. 1.e. 3 hours freezing and 3 hours at room temperature. The length of the working day allowed only two expos~lrc5

at one teniperature and one at the other: overnight ex- posure, therefore, alternated.

T o determine whether the low temperature had caused changes. the liquid coatings were examined visually and subjected to two physical tests. Consistency nieas~~renients made with the Stornier viscometer were ~lsed to follow the effect on the vehicle. If the binders were adversely a f - fected. the consistency would be expected to increase. Hiding power as measured by contrast ratio was used to I'ollow any changes in pigment dispersion. If the pigment or pigment-vehicle combination were ~lnstable. the hiding power should decrease because of pigment flocculation o r agglomeration.

RESULTS-No visual changes in the condition of the materials in the container were noted during the con- sistency and hiding power tests. Two materials tcsted for drying time were still satisfactory after exposure to low tcmperatLlfe.

Cot~.ti.ctetzcy trzeu.rLlretjletlt.c. provirlecl the tr1o.r.t infornia- tion on thc effects of continuous or alternating low tem- peratures. T h e changes in consistency after different cx- posures are given in Tnhle I. Fig~lre I illustrates the effects of the two cold tests on samples 1 and 3. T h e

BY G. A. O'DOHERTY a n d H. E. ASHTON O r g a n i c Materials Section Division of Building Research

National Research Council

algebraic mean for all tests is plotted in F i g ~ ~ r e 2. It niay be seen that the first exposure to continuous low temperature ( C L T ) had little effect on consistency. The mean change was less than 2 Krebs nits with about equal numbers increasing and decreasing. When some of the materials were exposed a second time to C L T the mean showed a noticeable increase in consistency. but this was influenced by one extreme value.

The cycling exposures caused greater consistcncy changes than did continuous exposure during the first 2- week period. Saniples exposed to cycling increased in consistency more during subsequent normal storage than did those that had been continuously frozen. T h e short (,-hour cycle was more severe than the 48-hour cycle altho~lgh, again, onc result markedly affected the mean. Of the different types of coatings the alkyd drum en;~mels showed the greatest changes. This result might be expected beca~lsc they are industrial finishes not neces- sarily formulated for long storage. The exterior paints showed the least change. but tho number of samples was too small to establish significi~nce. The 48-hour cycle had

a greater effect o n sample I than on sample 3. The former seemed more ~lnstable judging by the consistent). changes during latcr storage. Hence, this cycle might be ~ l s e f ~ l l in determining which materials would be most af- fected by low temperatures.

N o c o n c l ~ ~ s i o n s wer-c obtained from the hiding power tests d ~ ~ e to large, apparently random variations in the results. The variations occurred because when the tests were run the contrast ratio ~iiethod was fairly new ant1 not fully developecl. Since then i t has been improved and in the ASTM inter-laboratory test on hiding power by contrast ratio thc results reported to the 1966 meetings showed good agreement.

CONCLUSIONS-Contin~~ous exposure to low temperE1- tures is not deleterious to solvent-based coatings as evi- denced by consistency measurements. which mainly reflect thc condition of the vehicle. The general appcar- ancc also indicated satisfactory stability. This is to bc expected since the rates of chemical reactions decrease as tcmpcratures arc lowercd. As with water-based coatings. alternate freezing and thawing is more damaging, particu- larly to materials that are somewhat ~ ~ n s t a b l e . F r o m com- parisons made between consistcncy changes o c c ~ ~ r r i n g dur-

ing normal storage and accelerated tests, the 48-hour cycle charge o f the Paint Laboratory. Most of the laboratory is the best short-term test for predicting low temperature tests were performed by R. C. Seeley.

stability. The 6-hour cycle is too severe and CLT is not (This paper is a contributiorz frot~z the _{Divisorr of}

drastic enough for this purpose. B~~ildirlg Research, Natiorial Research Co~cncil, Canada, ACKNOWLEDGEMENT-This study was carried out a i d is p~~blished with the approval of the director o f the under the direction of John Harris, formerly officer in division.)

Normal storage

.-.-

I-',

Sample 1, cont. low temp

TIME. WEEKS TIME, WEEKS

Fig. 1

-

Effect of cold tests on two samples Fig. 2

-

Mean effect of cold tests.

TABLE I

Changes in Consistency in Krebs Units

Second Exposure to Low Temperature

First Exposure to Normal Storage 6 hr. Cycle

Sample Type of Low Temperature C.L.T. 48 hr. C.L.T. 48 hr. C.L.T. New

Number Material C.L.T. 48 hr. Cycle Sample Sample Sample Cycle Sample Sample

Drum Enamel

. . . .

Drum Enamel . . . . Drum Enamel

. . . .

Drum Enamel

. . . .

D r ~ ~ n i Enamel

. . . .

Drum Enamel

. . . .

Drum Enamel

. . . .

Drum Enamel

. . . .

Drum Enamel

. . . .

Drum Enamel

. . . .

Drum Enamel

. . . .

Automotive Enamel Automotive Enamel Automotive Enamel Laquer

. . .

Laquer

. . .

House Paint

. . .

House Paint

. . .

Exterior Paint . . . . House Paint

. . .

Mean Change

. . .

1.6 3.9 4.0 6.5 4.2 5.3 4.7 11.5

Algebraic Mean Change

.

-0.2

+

3.7 +2.8

+

6.5

+

3.8

.

+5.3 $4.7 f11.5

Group Mean

. . .

5.1 8.5

':: New material at time of second tests; subjected to 6-hr. cycle after only one exposure to C.L.T.

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